Blood lead in the normal range (less than 40 micron g/dl) has been found, in the investigator's studies of urban children, to be associated with a linear inhibition of Na/K ATPase activity of the rbc (red blood cell) membrane (ES 00939-01). The investigations during the current year (ES 00939-02) focus on the evidence for accelerated rbc hemolysis in association with inhibition of rbc Na/K ATPase, the enzyme primarily responsible for cation transport and integrity of the membrane. An increase in red cell hexokinase and glutamic oxalacetic transminase (GOT) are accepted as indicators of shortened rbc life span. Studies are almost complete of the relation of blood lead to these two indices and to pre-existing disorders of t(e rbc in 200 urban children: 50 control, 50 with iron deficiency anemia, 50 with G-6PD deficiency, and 50 with sickle cell trait (Hgb S/A). The third year of the project centers on: 1) the inhibition of rbc membrane Na/K ATPase by urban levels of lead as related to the health effect of altered osmotic fragility of the rbc in these children, and 2) the correlation of blood lead with platelet Na/K ATPase. A decrease in platelet Na/K ATPase has been associated with impaired uptake of serotonin (5HT) by platelets. The serotonin uptake of platelets has been proposed as a model for the neuronal uptake of 5HT, and demonstration of the effects of lead on the platelet enzyme can provide a peripheral index of the enurotoxicity of low level lead.